The present invention relates generally to a liquid level detector and more particularly to a liquid level detector utilizing an air dielectric transmission line and an R. F bridge.
Although many different types of liquid level sensors are known, a continuing need exists for a sensor which is suitable for use in hostile environments, reliable, and accurate over large measurement ranges. Such a sensor would be especially useful in measuring the coolant level in a nuclear reactor, where the reactor core must be immersed in coolant at all times. Should the coolant level fall below the top of the core, the reactor operators must be warned in order that they may take necessary steps to prevent a core meltdown.
One previous liquid level measuring system that has been developed for use with nuclear reactor cooling systems is shown in U.S. Pat. No. 4,170,135 by Glen Booman et al. In this patent, an air dielectric coaxial transmission line is lowered within the container containing the liquid to be measured. The fundamental resonant frequency of the portion of the coaxial cavity which does not contain liquid is inferred from several measurements of the harmonically related cavity resonances. The fundamental resonant frequency is then used to calculate the length of the liquid-free portion of the coaxial cavity and, thereby, the level of liquid in the container. As a resonant system, the Booman sensor must be operated at frequencies which are determined by the geometry of the probe itself. In addition, a readout of the distance requires some calculation, usually with a computer.